Skin abscess
Pus needs to come out. Incision and drainage is the treatment; antibiotics only for spreading cellulitis or an unwell patient.
A 32-year-old man has a 4 cm red, hot, fluctuant swelling on his thigh for 5 days. He has no fever. His blood glucose is 15.5 mmol/L (279 mg/dL).
A 56-year-old woman has a hot, tender swelling at the inner thigh. She is feverish, pulse 118 and BP 92/58, and the skin around it is dusky with crackling under the fingers.
Which one do you drain in clinic, and which needs theatre now?
- Is it an abscess?Fluctuant, pointing, or pus on ultrasound.
- Check glucoseRecurrent or large abscesses: diabetes.
- Incision and drainageThe main treatment. Local anaesthetic, incise along skin lines, break loculi, irrigate.
- Antibiotics only ifSurrounding cellulitis over 2 cm, systemic illness, immunosuppressed, diabetic, face or hand, or very young or old.
- Sepsis, skin necrosis, crepitus, pain out of proportionNecrotising fasciitis: surgeons now.
- Wound carePacking is often not needed for small abscesses. Daily dressings.
- RecurrentLook for PVL-staph, diabetes, hidradenitis.
- Sepsis
- Necrotising fasciitis signs
- Perianal abscess (theatre)
- Breast abscess
- Face (central triangle) or hand abscess
- Abscess near a large vessel (groin, neck)
- Necrotising fasciitis
- Diabetes
- Femoral artery pseudoaneurysm in injecting drug users (groin)
- Hidradenitis suppurativa
- Pilonidal disease
- Perianal fistula
| Abscess size for drainage | Usually 1 cm or more with fluctuance |
| Flucloxacillin | 500 mg–1 g every 6 hours for 5–7 days |
| Clindamycin | 300–450 mg every 6 hours (penicillin allergy) |
| Glucose check | Random above 11.1 mmol/L (200 mg/dL) suggests diabetes |
| Lidocaine | Up to 3 mg/kg (field block around the abscess) |
Check every dose against a current drug reference and your hospital protocol.
On this page
Abscess or cellulitis?
Abscess: drain
Cellulitis: antibiotics, mark the edge, review
Necrotising fasciitis: surgeons now
Groin swelling in someone who injects drugs: ultrasound first. It may be a pseudoaneurysm of the femoral artery. Never incise a pulsatile mass.
Incision and drainage
- Consent and analgesiaExplain pain, scarring, recurrence.
- AnaestheticField block around the abscess (local anaesthetic works poorly in pus). Sedation or general anaesthetic for large or deep ones.
- InciseOver the most fluctuant point, along skin lines, long enough to drain fully.
- Break loculiWith a finger or clip.
- Swab and irrigateSend pus for culture if recurrent, severe or unusual.
- Pack or notSmall abscesses often need no packing. Large cavities: loose packing for 24–48 hours.
- DressingAbsorbent, changed daily.
Sites needing specialist care
| Site | Why | Who |
|---|---|---|
| Perianal | Fistula, sphincters | General surgeons, theatre |
| Breast | Ultrasound-guided aspiration often first | Breast surgeons |
| Hand | Tendon sheaths, spaces | Hand surgeons |
| Face (central triangle) | Venous drainage to cavernous sinus | Senior, IV antibiotics |
| Neck | Deep spaces, airway | ENT |
| Pilonidal | Recurrence, sinus | Surgeons |
Recurrent abscesses
- Check glucose and HbA1c.
- PVL-producing Staph aureus: recurrent boils in close contacts; send pus, decolonise if positive.
- Hidradenitis suppurativa: armpits, groins, under breasts, with scarring and sinuses.
- Look for other causes: poor hygiene, immunosuppression, foreign body.
Investigations
| Test | Why |
|---|---|
| Blood glucose, HbA1c | Diabetes |
| Pus culture | Recurrent, severe, immunosuppressed |
| FBC, CRP, lactate, blood cultures | Systemic infection |
| Ultrasound | Collection unclear, groin swellings |
| CT | Deep collections, necrotising infection (don't delay surgery) |
Treatment
See cellulitis and sepsis.
Common mistakes
- Treating an abscess with antibiotics alone.
- Incising a groin swelling in an injecting drug user without ultrasound.
- Missing necrotising fasciitis (pain out of proportion).
- Making the incision too small.
- Not checking glucose.
- Draining a perianal abscess in clinic.
Frequently asked questions
What is the treatment for a skin abscess?
Incision and drainage. Antibiotics are added only with significant cellulitis, systemic illness or other risk factors.
Does an abscess need packing?
Small abscesses often heal well without packing. Larger cavities may be loosely packed for 24–48 hours.
What should be checked in recurrent abscesses?
Blood glucose and HbA1c, pus culture for PVL-producing Staph aureus, and signs of hidradenitis suppurativa.
When is a skin abscess an emergency?
With sepsis, necrotising fasciitis signs (dusky skin, crepitus, severe pain), or at high-risk sites such as the perianal area, hand or central face.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A fluctuant buttock abscess in a well patient. What is the main treatment?
Answer: Incision and drainage. Antibiotics are added only for cellulitis, systemic signs or high-risk patients.
- Steroid injection: No.
- Antibiotics alone: Pus needs drainage.
- Warm compress only: Not for fluctuant abscess.
- Needle aspiration only: Less effective.
2. A man has recurrent boils. Which test should be done?
Answer: Blood glucose. Diabetes predisposes to recurrent skin infections.
- Chest X-ray: No.
- Stool culture: No.
- ESR: Not specific.
- Thyroid function: Less relevant.
3. Which is a high-risk abscess site needing specialist care?
Answer: Perianal. Perianal, central facial, breast and hand abscesses need specialist care.
- Thigh: Usually simple.
- Forearm: Usually simple.
- Back: Usually simple.
- Upper arm: Usually simple.
4. A sexually active young woman has a urinary tract infection with a Gram-positive, coagulase-negative coccus resistant to novobiocin. What is the organism?
Answer: Staphylococcus saprophyticus. Coagulase-negative staphylococci: S. epidermidis (novobiocin-sensitive; biofilms on catheters, prosthetic valves) and S. saprophyticus (novobiocin-resistant; second commonest cause of UTI in young sexually active women after E. coli). S. aureus is coagulase-positive. Enterococci are catalase-negative.
- Staphylococcus epidermidis: Novobiocin-sensitive; device infections.
- Staphylococcus aureus: Coagulase-positive.
- Enterococcus faecalis: Catalase-negative.
- Streptococcus agalactiae: Catalase-negative; neonatal sepsis.
5. Which antibiotic used for MRSA can cause thrombocytopenia and serotonin syndrome with SSRIs?
Answer: Linezolid. Linezolid (oxazolidinone; binds 23S rRNA of the 50S subunit, preventing initiation complex formation) treats MRSA and VRE, with good oral bioavailability. It is a weak MAO inhibitor (serotonin syndrome with SSRIs, tyramine reactions) and causes myelosuppression (especially thrombocytopenia) and peripheral/optic neuropathy with prolonged use. Daptomycin causes myopathy (raised CK) and is inactivated by surfactant (not for pneumonia).
- Vancomycin: Red-man syndrome, nephrotoxicity.
- Daptomycin: Myopathy; not for pneumonia.
- Teicoplanin: Glycopeptide; similar to vancomycin.
- Clindamycin: C. difficile risk.
References and dose sources
- NICE CKS — Boils, carbuncles and staphylococcal carriage
- NICE NG141 — Cellulitis (if surrounding infection)
- Lidocaine (lignocaine) dosing: Drugs.com: Lidocaine dosage (see also our lidocaine (lignocaine) dose page)
- Flucloxacillin dosing: Drugs.com: Flucloxacillin (international) (see also our flucloxacillin dose page)
- Clindamycin dosing: Drugs.com: Clindamycin dosage (see also our clindamycin dose page)
- Paracetamol dosing: Drugs.com: Acetaminophen (paracetamol) dosage (see also our paracetamol dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.